if it is a different system than yours and is a factory restore cd it won't work......i.e. dell on a hp but if it is a regular windows xp cd and the same version of pro and not home and both came from the factory with the same service pack then it should install with the keys on the side of the case.
make sure you both have the same version of windows or you'll be out of luck.. you can still activate it it just takes calling microsoft and telling them you upgraded your hard drive from a crash